The Nuclear Densitometer: Its Design, Use in Construction, and an Experimental Application — The Independent Study project of Addie Tagg (’23)

Editor’s Note: Independent Study (IS) at The College of Wooster is a three-course series required of every student before graduation. Earth Sciences students typically begin in the second semester of their junior years with project identification, literature review, and a thesis essentially setting out the hypotheses and parameters of the work. Most students do fieldwork or lab work to collect data, and then spend their senior years finishing extensive Senior I.S. theses. Addie Tagg was advised by Mark Wilson (me!). The following is her thesis abstract —

The nuclear densitometer, or nuclear gauge, is a tool that is used to take the most accurate measurements of density and moisture content in soils, aggregates, and other materials. These measurements are used for many aspects of construction. The gauge takes density measurements based on the radioactive source Cesium-137. Key concepts for understanding how the gauge operates include photoelectric absorption, Compton scattering, and pair production. It is impossible to measure the reaction of a beam through a material, but it is possible to calculate the percentage of a source that is absorbed. The source that is not absorbed is reflected. The denser that a soil is, fewer waves are detected. After the device is calibrated and the number of reflected particles is counted, this number can then be translated into wet density. Alternative methods of recording density include the dynamic cone penetrometer and sand replacement. Overall, the nuclear densitometer is the easiest and least destructive method of density testing. The gauge does not directly measure water content, but instead measures hydrogen. This fact led me to an experiment to inquire if a common household weed killer would affect the gauge’s ability to take accurate measurements. The experiment included three trials using two layers of crushed limestone, each with a different substance applied (dry stone, water, or weed killer), compacted with a hand tamper and measured for compaction with the nuclear gauge. Overall, the weed killer did not affect the gauge’s ability to take an accurate measurement.

About Mark Wilson

Mark Wilson is a Professor of Geology at The College of Wooster. He specializes in invertebrate paleontology, carbonate sedimentology, and stratigraphy. He also is an expert on pseudoscience, especially creationism.
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